(1) Field of the Invention
The invention relates to a method for determining two pseudo-sinusoidal signals in quadrature from a pseudo-sinusoidal signal transmitted by an encoder, a system for determining by implementing such a method, as well as a bearing including such a determination system.
The invention applies in particular to the field of determining angular data, such as the position or the speed of a rotating member in relation to a stationary member.
(2) Prior Art
As a matter of fact, in an application such as this, it is necessary to be able to make advantageous use of two pseudo-sinusoidal signals in quadrature, which are representative of the angular position of the rotating member in relation to the stationary member.
In order to do so, it is known from the document FR-A1-2 792 403, to use an encoder capable of transmitting a pseudo-sinusoidal signal, and a sensor including at least four sensing elements which are linearly equally distributed, said sensing elements each being capable of delivering a signal Si representative of the signal transmitted by the encoder. In order to form the two signals in quadrature, this document anticipates combining the signals Si in order to form the signalsU=(S1−S2)−(S3−S4) and V=(S1+S2)−(S3+S4).
When it is implemented with a multipole encoder delivering a magnetic signal, this embodiment has numerous advantages in that it makes it possible:                to preserve the signals U and V in quadrature for several pole lengths of the encoder;        to obtain signals U and V of the same amplitude, for a given pole length, by adjusting the conditioning gains corresponding to the amplification of the signals U or V;        to eliminate the magnetic offsets.        
On the other hand, under certain particular operating conditions, this embodiment can introduce certain limitations with respect to the positioning of the sensing elements in relation to the encoder.
For example, the equality of the amplitudes of the signals U and V can be affected by:                a misalignment of the encoder in relation to its axis of rotation, which is the reason why the sensing elements detect poles of variable pole lengths in one revolution;        the presence of poles of different length on the encoder, whether this presence is due to a magnetization defect or to a desired configuration;        the application of a gain which is not perfectly suited to the pole length of the encoder.        
Furthermore, the quadrature of the signals U and V can be affected when the straight line passing through all of the sensing elements is not perfectly parallel to the plane of the encoder (tilt of the sensor) This phenomenon is all the more critical the more the amplitude of the magnetic field varies exponentially in relation to the distance between the encoder and the sensing element.
Finally, in the case where the sensing elements are not arranged along the tangent to the reading beam (twist of the sensor), the two phenomena described above are combined, namely:                the pole length seen by each of the sensing elements is different;        the amplitude of the magnetic field read by the sensing elements is not the same, because of the edge effects on the signal delivered.        